As device geometries continue to shrink, one of the challenges facing the semiconductor industry is the deposition of thin, continuous films for use as copper diffusion barriers and as seeds for electroplating. The inability to grow thin, continuous metal films by chemical vapor deposition or pulsed layer deposition is often due to the inability of the metal films to nucleate on the dielectric surface. This has been found to be especially true for depositing ruthenium on SiO2 It is believed that the process involves the chemisorption of a continuous layer of the nucleation catalyst on the dielectric surface followed by chemical deposition of the ruthenium films. This layer will be referred to throughout this application as a “catalytic nucleation layer”. It is believed that the presence of the amine ligand enhances the reactivity of the substrate towards ruthenocene molecules thereby allowing nucleation and coalescence of the ruthenium films to proceed more rapidly. The phenomenon is not well understood, but it is likely a combination of enhanced chemical reactivity of the treated surface towards the precursor module and a higher energy barrier to surface diffusion of the precursor molecule on the treated surface. This results in smaller and more densely populated nuclei in the early deposition stage. This also leads to reduced activation energy, which in turn leads to reduced deposition temperature.
Thus, one area of particular concern is efficient nucleation of deposited metal layers. “Nucleation” refers to the initial formation of metal nuclei on a substrate such as a dielectric layer. Often the process conditions present a kinetic barrier to formation of such nuclei. In such cases, there may be a delay in deposition between the time when the substrate is exposed to metal precursor and the time when the metal actually begins to form on the surface. The problem may also be manifested by higher substrate temperatures required to initiate nucleation during the process.
Additionally, current methods for the deposition of ruthenium on SiO2 form rough, non-uniform films, often with incomplete coverage.
What is needed, therefore, is a process for allowing a reduction in nucleation delay and improvement of morphology of ruthenium films.